Interface pressures during ambulation using suction
and vacuum-assisted prosthetic sockets

Tracy L. Beil, MS; Glenn M. Street, PhD; Steven J. Covey, PhD, PE

Human Performance Laboratory and the Department of Mechanical and Manufacturing Engineering, St. Cloud State University, MN

Abstract—Interface pressures were measured during ambulation
with a normal total-surface weight-bearing suction socket and a vacuum-assisted
socket. The vacuum-assisted socket has been shown to eliminate daily volume
loss. Urethane liners were instrumented with five force-sensing resistors
to measure positive pressures and one air pressure sensor at the distal end
of the liner to document negative pressures. Nine unilateral transtibial amputees
participated in the study. The vacuum-assisted socket created significantly
lower positive-pressure impulse (42.8, 39.6 kPa²s)
and peak pressures (83.5, 80.0 kPa) during the stance phase. The pressure
impulse (–10.5, –13.3 kPa²s),
average (–21.2, –26.5 kPa), and peak (–28.5, –36.3
kPa) negative pressures during swing phase were significantly greater in magnitude
with the vacuum-assisted socket. We believe that lower positive pressures
seen during stance using the vacuum-assisted socket reduces the fluid forced
out and greater negative pressures seen during swing increases the amount
of fluid drawn into the limb, thereby preventing volume loss.